Function

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Overview

Serine/threonine-protein kinase that acts downstream of ERK (MAPK1/ERK2 and MAPK3/ERK1) signaling and mediates mitogenic and stress-induced activation of the transcription factors CREB1, ETV1/ER81 and NR4A1/NUR77, regulates translation through RPS6 and EIF4B phosphorylation, and mediates cellular proliferation, survival, and differentiation by modulating mTOR signaling and repressing pro-apoptotic function of BAD and DAPK1. In fibroblast, is required for EGF-stimulated phosphorylation of CREB1 and histone H3 at 'Ser-10', which results in the subsequent transcriptional activation of several immediate-early genes. In response to mitogenic stimulation (EGF and PMA), phosphorylates and activates NR4A1/NUR77 and ETV1/ER81 transcription factors and the cofactor CREBBP. Upon insulin-derived signal, acts indirectly on the transcription regulation of several genes by phosphorylating GSK3B at 'Ser-9' and inhibiting its activity. Phosphorylates RPS6 in response to serum or EGF via an mTOR-independent mechanism and promotes translation initiation by facilitating assembly of the preinitiation complex. In response to insulin, phosphorylates EIF4B, enhancing EIF4B affinity for the EIF3 complex and stimulating cap-dependent translation. Is involved in the mTOR nutrient-sensing pathway by directly phosphorylating TSC2 at 'Ser-1798', which potently inhibits TSC2 ability to suppress mTOR signaling, and mediates phosphorylation of RPTOR, which regulates mTORC1 activity and may promote rapamycin-sensitive signaling independently of the PI3K/AKT pathway. Mediates cell survival by phosphorylating the pro-apoptotic proteins BAD and DAPK1 and suppressing their pro-apoptotic function. Promotes the survival of hepatic stellate cells by phosphorylating CEBPB in response to the hepatotoxin carbon tetrachloride (CCl4). Is involved in cell cycle regulation by phosphorylating the CDK inhibitor CDKN1B, which promotes CDKN1B association with 14-3-3 proteins and prevents its translocation to the nucleus and inhibition of G1 progression. In LPS-stimulated dendritic cells, is involved in TLR4-induced macropinocytosis, and in myeloma cells, acts as effector of FGFR3-mediated transformation signaling, after direct phosphorylation at Tyr-529 by FGFR3. Phosphorylates DAPK1.

BACKGROUND: The mammalian target of rapamycin (mTOR) is a Ser/Thr kinase that controls cell growth in response to mitogens, as well as amino acid and energy sufficiency. The scaffolding protein Raptor binds to mTOR and recruits substrates to the rapamycin-sensitive mTOR complex 1 (mTORC1). Although Raptor has been shown to be essential for mTORC1 activity, the mechanisms regulating Raptor function remain unknown. RESULTS: Here, we demonstrate that Raptor becomes highly phosphorylated on RXRXXpS/T consensus motifs after activation of the Ras/mitogen-activated protein kinase (MAPK) pathway. Using pharmacological inhibitors and RNA interference, we show that the p90 ribosomal S6 kinases (RSKs) 1 and 2 are required for Raptor phosphorylation in vivo and directly phosphorylate Raptor in vitro. Quantitative mass spectrometry and site-directed mutagenesis revealed that RSK specifically phosphorylates Raptor within an evolutionarily conserved region with no previously known function. Interestingly, expression of oncogenic forms of Ras and MEK that elevate mTORC1 activity induced strong and constitutive phosphorylation of Raptor on these residues. Importantly, we demonstrate that expression of Raptor mutants lacking RSK-dependent phosphorylation sites markedly reduced mTOR phosphotransferase activity, indicating that RSK-mediated phosphorylation of Raptor is important for mTORC1 activation by the Ras/MAPK pathway. CONCLUSIONS: We propose a unique mode of mTOR regulation in which RSK-mediated phosphorylation of Raptor regulates mTORC1 activity and thus suggest a means by which the Ras/MAPK pathway might promote rapamycin-sensitive signaling independently of the PI3K/Akt pathway.

Converging signals from the mammalian target of rapamycin (mTOR) and phosphoinositide 3-kinase (PI3K) pathways are well established to modulate translation initiation. Less is known regarding the molecular basis of protein synthesis regulated by other inputs, such as agonists of the Ras/extracellular signal-regulated kinase (ERK) signaling cascade. Ribosomal protein (rp) S6 is a component of the 40S ribosomal subunit that becomes phosphorylated at several serine residues upon mitogen stimulation, but the exact molecular mechanisms regulating its phosphorylation and the function of phosphorylated rpS6 is poorly understood. Here, we provide evidence that activation of the p90 ribosomal S6 kinases (RSKs) by serum, growth factors, tumor promoting phorbol esters, and oncogenic Ras is required for rpS6 phosphorylation downstream of the Ras/ERK signaling cascade. We demonstrate that while ribosomal S6 kinase 1 (S6K1) phosphorylates rpS6 at all sites, RSK exclusively phosphorylates rpS6 at Ser(235/236) in vitro and in vivo using an mTOR-independent mechanism. Mutation of rpS6 at Ser(235/236) reveals that phosphorylation of these sites promotes its recruitment to the 7-methylguanosine cap complex, suggesting that Ras/ERK signaling regulates assembly of the translation preinitiation complex. These data demonstrate that RSK provides an mTOR-independent pathway linking the Ras/ERK signaling cascade to the translational machinery.

Nur77 is a nuclear orphan receptor that is able to activate transcription independently of exogenous ligand, and has also been shown to promote apoptosis on its localization to mitochondria. Phosphorylation of Nur77 on Ser354 has been suggested to reduce ability of Nur77 to bind DNA; however, the kinase responsible for this phosphorylation in cells has not been clearly established. In the present study, we show that Nur77 is phosphorylated on this site by RSK (ribosomal S6 kinase) and MSK (mitogen- and stress-activated kinase), but not by PKB (protein kinase B) or PKA (protein kinase A), in vitro. In cells, phosphorylation of Nur77 in vivo is catalysed by RSK, which is activated downstream of the classical MAPK (mitogen-activated protein kinase) cascade. Phosphorylation of Nur77 by RSK is able to promote the binding of Nur77 to 14-3-3 proteins in vitro, however, no evidence could be seen for this interaction in cells. We have established that two related proteins, Nurr1 and Nor1, are also phosphorylated on the equivalent site by RSK in cells in response to mitogenic stimulation.

The viability of vertebrate cells depends on a complex signaling interplay between survival factors and cell-death effectors. Subtle changes in the equilibrium between these regulators can result in abnormal cell proliferation or cell death, leading to various pathological manifestations. Death-associated protein kinase (DAPK) is a multidomain calcium/calmodulin (CaM)-dependent Ser/Thr protein kinase with an important role in apoptosis regulation and tumor suppression. The molecular signaling mechanisms regulating this kinase, however, remain unclear. Here, we show that DAPK is phosphorylated upon activation of the Ras-extracellular signal-regulated kinase (ERK) pathway. This correlates with the suppression of the apoptotic activity of DAPK. We demonstrate that DAPK is a novel target of p90 ribosomal S6 kinases (RSK) 1 and 2, downstream effectors of ERK1/2. Using mass spectrometry, we identified Ser-289 as a novel phosphorylation site in DAPK, which is regulated by RSK. Mutation of Ser-289 to alanine results in a DAPK mutant with enhanced apoptotic activity, whereas the phosphomimetic mutation (Ser289Glu) attenuates its apoptotic activity. Our results suggest that RSK-mediated phosphorylation of DAPK is a unique mechanism for suppressing the proapoptotic function of this death kinase in healthy cells as well as Ras/Raf-transformed cells.

During the immediate-early response of mammalian cells to mitogens, histone H3 is rapidly and transiently phosphorylated by one or more unidentified kinases. Rsk-2, a member of the pp90rsk family of kinases implicated in growth control, was required for epidermal growth factor (EGF)-stimulated phosphorylation of H3. RSK-2 mutations in humans are linked to Coffin-Lowry syndrome (CLS). Fibroblasts derived from a CLS patient failed to exhibit EGF-stimulated phosphorylation of H3, although H3 was phosphorylated during mitosis. Introduction of the wild-type RSK-2 gene restored EGF-stimulated phosphorylation of H3 in CLS cells. In addition, disruption of the RSK-2 gene by homologous recombination in murine embryonic stem cells abolished EGF-stimulated phosphorylation of H3. H3 appears to be a direct or indirect target of Rsk-2, suggesting that chromatin remodeling might contribute to mitogen-activated protein kinase-regulated gene expression.

Activation by growth factors of the Ras-dependent signaling cascade results in the induction of p90 ribosomal S6 kinases (p90(rsk)). These are translocated into the nucleus upon phosphorylation by mitogen-activated protein kinases, with which p90(rsk) are physically associated in the cytoplasm. In humans there are three isoforms of the p90(rsk) family, Rsk-1, Rsk-2, and Rsk-3, which are products of distinct genes. Although these isoforms are structurally very similar, little is known about their functional specificity. Recently, mutations in the Rsk-2 gene have been associated with the Coffin-Lowry syndrome (CLS). We have studied a fibroblast cell line established from a CLS patient that bears a nonfunctional Rsk-2. Here we document that in CLS fibroblasts there is a drastic attenuation in the induced Ser-133 phosphorylation of transcription factor CREB (cAMP response element-binding protein) in response to epidermal growth factor stimulation. The effect is specific, since response to serum, cAMP, and UV light is unaltered. Furthermore, epidermal growth factor-induced expression of c-fos is severely impaired in CLS fibroblasts despite normal phosphorylation of serum response factor and Elk-1. Finally, coexpression of Rsk-2 in transfected cells results in the activation of the c-fos promoter via the cAMP-responsive element. Thus, we establish a link in the transduction of a specific growth factor signal to changes in gene expression via the phosphorylation of CREB by Rsk-2.

The beta-isoform of glycogen synthase kinase-3 (GSK3 beta) isolated from rabbit skeletal muscle was inactivated 90-95% following incubation with MgATP and either MAP kinase-activated protein kinase-1 (MAPKAP kinase-1, also termed RSK-2) or p70 S6 kinase (p70S6K), and re-activated with protein phosphatase 2A. MAPKAP kinase-1 and p70S6K phosphorylated the same tryptic peptide on GSK3 beta, and the site of phosphorylation was identified as the serine located nine residues from the N-terminus of the protein. The inhibitory effect of Ser-9 phosphorylation on GSK3 beta activity was observed with three substrates, (inhibitor-2, c-jun and a synthetic peptide), and also with glycogen synthase provided that 0.15 M KCl was added to the assays. The results suggest that Ser-9 phosphorylation underlies the reported inhibition of GSK3 beta by insulin and that GSK3 may represent a point of convergence of two major growth-factor-stimulated protein kinase cascades.

Signal transduction pathways in the cell require protein-protein interactions (PPIs) to respond to environmental cues. Diverse experimental techniques for detecting PPIs have been developed. However, the huge amount of PPI data accumulated from various sources poses a challenge with respect to data reliability. Herein, we collected ∼700 primary antibodies and employed a highly sensitive and specific technique, an in situ proximity ligation assay, to investigate 1204 endogenous PPIs in HeLa cells, and 557 PPIs of them tested positive. To overview the tested PPIs, we mapped them into 13 PPI public databases, which showed 72% of them were annotated in the Human Protein Reference Database (HPRD) and 8 PPIs were new PPIs not in the PubMed database. Moreover, TP53, CTNNB1, AKT1, CDKN1A, and CASP3 were the top 5 proteins prioritized by topology analyses of the 557 PPI network. Integration of the PPI-pathway interaction revealed that 90 PPIs were cross-talk PPIs linking 17 signaling pathways based on Reactome annotations. The top 2 connected cross-talk PPIs are MAPK3-DAPK1 and FAS-PRKCA interactions, which link 9 and 8 pathways, respectively. In summary, we established an open resource for biological modules and signaling pathway profiles, providing a foundation for comprehensive analysis of the human interactome.

Cellular information processing via reversible protein phosphorylation requires tight control of the localization, activity, and substrate specificity of protein kinases, which to a large extent is accomplished by complex formation with other proteins. Despite their critical role in cellular regulation and pathogenesis, protein interaction information is available for only a subset of the 518 human protein kinases. Here we present a global proteomic analysis of complexes of the human CMGC kinase group. In addition to subgroup-specific functional enrichment and modularity, the identified 652 high-confidence kinase-protein interactions provide a specific biochemical context for many poorly studied CMGC kinases. Furthermore, the analysis revealed a kinase-kinase subnetwork and candidate substrates for CMGC kinases. Finally, the presented interaction proteome uncovered a large set of interactions with proteins genetically linked to a range of human diseases, including cancer, suggesting additional routes for analyzing the role of CMGC kinases in controlling human disease pathways.

Proteome-scale protein interaction maps are available for many organisms, ranging from bacteria, yeast, worms and flies to humans. These maps provide substantial new insights into systems biology, disease research and drug discovery. However, only a small fraction of the total number of human protein-protein interactions has been identified. In this study, we map the interactions of an unbiased selection of 5026 human liver expression proteins by yeast two-hybrid technology and establish a human liver protein interaction network (HLPN) composed of 3484 interactions among 2582 proteins. The data set has a validation rate of over 72% as determined by three independent biochemical or cellular assays. The network includes metabolic enzymes and liver-specific, liver-phenotype and liver-disease proteins that are individually critical for the maintenance of liver functions. The liver enriched proteins had significantly different topological properties and increased our understanding of the functional relationships among proteins in a liver-specific manner. Our data represent the first comprehensive description of a HLPN, which could be a valuable tool for understanding the functioning of the protein interaction network of the human liver.

During the immediate-early response of mammalian cells to mitogens, histone H3 is rapidly and transiently phosphorylated by one or more unidentified kinases. Rsk-2, a member of the pp90rsk family of kinases implicated in growth control, was required for epidermal growth factor (EGF)-stimulated phosphorylation of H3. RSK-2 mutations in humans are linked to Coffin-Lowry syndrome (CLS). Fibroblasts derived from a CLS patient failed to exhibit EGF-stimulated phosphorylation of H3, although H3 was phosphorylated during mitosis. Introduction of the wild-type RSK-2 gene restored EGF-stimulated phosphorylation of H3 in CLS cells. In addition, disruption of the RSK-2 gene by homologous recombination in murine embryonic stem cells abolished EGF-stimulated phosphorylation of H3. H3 appears to be a direct or indirect target of Rsk-2, suggesting that chromatin remodeling might contribute to mitogen-activated protein kinase-regulated gene expression.

The progression of biochemical and morphological phases and events that occur in a cell during successive cell replication or nuclear replication events. Canonically, the cell cycle comprises the replication and segregation of genetic material followed by the division of the cell, but in endocycles or syncytial cells nuclear replication or nuclear division may not be followed by cell division.

The process whose specific outcome is the progression of the central nervous system over time, from its formation to the mature structure. The central nervous system is the core nervous system that serves an integrating and coordinating function. In vertebrates it consists of the brain and spinal cord. In those invertebrates with a central nervous system it typically consists of a brain, cerebral ganglia and a nerve cord.

The process in which a signal is passed on to downstream components within the cell, which become activated themselves to further propagate the signal and finally trigger a change in the function or state of the cell.

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases that regulate diverse cellular processes, such as cell growth, cell motility, cell survival and cell proliferation. RSKs are downstream effectors of the Ras-extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling cascade. Significant advances in the field of RSK and ERK/MAPK signalling have occurred in the past few years, including biological insights and the discovery of novel substrates and new RSK regulatory mechanisms. Collectively, these data expand the current models of RSK signalling and highlight potential directions of research in RSK-mediated survival, growth, proliferation and migration.

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases that regulate diverse cellular processes, such as cell growth, cell motility, cell survival and cell proliferation. RSKs are downstream effectors of the Ras-extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling cascade. Significant advances in the field of RSK and ERK/MAPK signalling have occurred in the past few years, including biological insights and the discovery of novel substrates and new RSK regulatory mechanisms. Collectively, these data expand the current models of RSK signalling and highlight potential directions of research in RSK-mediated survival, growth, proliferation and migration.

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases that regulate diverse cellular processes, such as cell growth, cell motility, cell survival and cell proliferation. RSKs are downstream effectors of the Ras-extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling cascade. Significant advances in the field of RSK and ERK/MAPK signalling have occurred in the past few years, including biological insights and the discovery of novel substrates and new RSK regulatory mechanisms. Collectively, these data expand the current models of RSK signalling and highlight potential directions of research in RSK-mediated survival, growth, proliferation and migration.

Oncogenic mutations of ras and B-raf frequently occur in many cancer types and are critical for cell transformation and tumorigenesis. Death receptor 5 (DR5) is a cell surface pro-apoptotic death receptor for tumor necrosis factor-related apoptosis-inducing ligand and has been targeted in cancer therapy. The current study has demonstrated induction of DR5 expression by the oncogenic proteins Ras and B-Raf and revealed the underlying mechanisms. We demonstrated that both Ras and B-Raf induce DR5 expression by enforced expression of oncogenic Ras (e.g. H-Ras12V or K-Ras12V) or B-Raf (i.e. V600E) in cells and by analyzing gene expression array data generated from cancer cell lines and from human cancer tissues. This finding is further supported by our results that knockdown of endogenous K-Ras or B-Raf (V600E) reduced the expression of DR5. Importantly, we have elucidated that Ras induces DR5 expression through co-activation of ERK/RSK and JNK signaling pathways and subsequent cooperative effects among the transcriptional factors CHOP, Elk1, and c-Jun to enhance DR5 gene transcription. Moreover, we found that the majority of cancer cell lines highly sensitive to the DR5 agonistic antibody AMG655 have either Ras or B-Raf mutations. Our findings warrant further study on the biology of DR5 regulation by Ras and B-Raf, which may provide new insight into the biology of Ras and B-Raf, and on the potential impact of Ras or B-Raf mutations on the outcome of DR5-targeted cancer therapy.

Modulation of the frequency, rate or extent of transcription from a DNA template as a result of a stimulus indicating the organism is under stress. The stress is usually, but not necessarily, exogenous (e.g. temperature, humidity, ionizing radiation).

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases that regulate diverse cellular processes, such as cell growth, cell motility, cell survival and cell proliferation. RSKs are downstream effectors of the Ras-extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling cascade. Significant advances in the field of RSK and ERK/MAPK signalling have occurred in the past few years, including biological insights and the discovery of novel substrates and new RSK regulatory mechanisms. Collectively, these data expand the current models of RSK signalling and highlight potential directions of research in RSK-mediated survival, growth, proliferation and migration.

Modulation of the frequency, rate or extent of translation as a result of a stimulus indicating the organism is under stress. The stress is usually, but not necessarily, exogenous (e.g. temperature, humidity, ionizing radiation).

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases that regulate diverse cellular processes, such as cell growth, cell motility, cell survival and cell proliferation. RSKs are downstream effectors of the Ras-extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling cascade. Significant advances in the field of RSK and ERK/MAPK signalling have occurred in the past few years, including biological insights and the discovery of novel substrates and new RSK regulatory mechanisms. Collectively, these data expand the current models of RSK signalling and highlight potential directions of research in RSK-mediated survival, growth, proliferation and migration.

Any process that results in a change in state or activity of an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a lipopolysaccharide stimulus; lipopolysaccharide is a major component of the cell wall of gram-negative bacteria.

The cellular process in which a signal is conveyed to trigger a change in the activity or state of a cell. Signal transduction begins with reception of a signal (e.g. a ligand binding to a receptor or receptor activation by a stimulus such as light), or for signal transduction in the absence of ligand, signal-withdrawal or the activity of a constitutively active receptor. Signal transduction ends with regulation of a downstream cellular process, e.g. regulation of transcription or regulation of a metabolic process. Signal transduction covers signaling from receptors located on the surface of the cell and signaling via molecules located within the cell. For signaling between cells, signal transduction is restricted to events at and within the receiving cell.

During the immediate-early response of mammalian cells to mitogens, histone H3 is rapidly and transiently phosphorylated by one or more unidentified kinases. Rsk-2, a member of the pp90rsk family of kinases implicated in growth control, was required for epidermal growth factor (EGF)-stimulated phosphorylation of H3. RSK-2 mutations in humans are linked to Coffin-Lowry syndrome (CLS). Fibroblasts derived from a CLS patient failed to exhibit EGF-stimulated phosphorylation of H3, although H3 was phosphorylated during mitosis. Introduction of the wild-type RSK-2 gene restored EGF-stimulated phosphorylation of H3 in CLS cells. In addition, disruption of the RSK-2 gene by homologous recombination in murine embryonic stem cells abolished EGF-stimulated phosphorylation of H3. H3 appears to be a direct or indirect target of Rsk-2, suggesting that chromatin remodeling might contribute to mitogen-activated protein kinase-regulated gene expression.

The process whose specific outcome is the progression of the skeleton over time, from its formation to the mature structure. The skeleton is the bony framework of the body in vertebrates (endoskeleton) or the hard outer envelope of insects (exoskeleton or dermoskeleton).

The Coffin-Lowry syndrome (CLS), an X-linked disorder, is characterized by severe psychomotor retardation, facial and digital dysmorphisms, and progressive skeletal deformations. Genetic linkage analysis mapped the CLS locus to an interval of 2-3 megabases at Xp22.2. The gene coding for Rsk-2, a member of the growth-factor-regulated protein kinases, maps within the candidate interval, and was tested as a candidate gene for CLS. Initial screening for mutations in the gene for Rsk-2 in 76 unrelated CLS patients revealed one intragenic deletion, a nonsense, two splice site, and two missense mutations. The two missenses affect sites critical for the function of Rsk-2. The mutated Rsk-2 proteins were found to be inactive in a S6 kinase assay. These findings provide direct evidence that abnormalities in the MAPK/RSK signalling pathway cause Coffin-Lowry syndrome.

Any series of molecular signals generated as a consequence of binding to a toll-like receptor. Toll-like receptors directly bind pattern motifs from a variety of microbial sources to initiate innate immune response.

Upon extracellular signal or mitogen stimulation, phosphorylated at Thr-577 in the C-terminal kinase domain (CTKD) by MAPK1/ERK2 and MAPK3/ERK1. The activated CTKD then autophosphorylates Ser-386, allowing binding of PDPK1, which in turn phosphorylates Ser-227 in the N-terminal kinase domain (NTDK) leading to the full activation of the protein and subsequent phosphorylation of the substrates by the NTKD.

Keywords

Protein involved in the complex series of events by which the cell duplicates its contents and divides into two. The eukaryotic cell cycle can be divided in four phases termed G1 (first gap period), S (synthesis, phase during which the DNA is replicated), G2 (second gap period) and M (mitosis). The prokaryotic cell cycle typically involves a period of growth followed by DNA replication, partition of chromosomes, formation of septum and division into two similar or identical daughter cells.

Protein involved in the response to stress, a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of some stressful conditions. The stress is usually, but not necessarily, exogenous (e.g. temperature, humidity, ionizing radiation, hypertonicity, amino acid deprivation).

Protein which catalyzes the phosphorylation of serine or threonine residues on target proteins by using ATP as phosphate donor. Such phosphorylation may cause changes in the function of the target protein. Protein kinases share a conserved catalytic core common to both serine/ threonine and tyrosine protein kinases.

Protein which is part of a reference proteome. Reference proteomes are a subset of proteomes that have been selected either manually or algorithmically according to a number of criteria to provide a broad coverage of the tree of life and a representative cross-section of the taxonomic diversity found within UniProtKB, as well as the proteomes of well-studied model organisms and other species of interest for biomedical research.